Cryopumping installations with high flow-rates

ABSTRACT

A cryopump is constituted by a fluidtight casing inside which is arranged a plurality of condensation plates carried by a cooling coil supplied with very cold fluid, the whole disposed externally of and around a baffle formed by a plurality of frustoconical rings arranged in the extension of a stop valve. The baffle is preferably cooled by a moderately cold fluid (80* K) though conduits, while a coil embedded in the wall of the casing and traversed by a moderately cold fluid cools an internal wall of the casing. This cryopumping device is adapted to extract high flow rates at a relatively moderate pressure of the order of 10 2 torr.

United States Patent [72] Inventor Michel Rapinat Fontaine, France [2l]Appl. No. 840,734 [22] Filed July 10, 1969 [4S Patented May 25, 1971[73] Assignee L`Air Liquide, Societe Anonyme pour Letude etLexploitation des procedes Georges Claude [32] Priority July 30, 1968[33] France [3 l 16 1,16 l

[54] CRYOPUMPING INSTALLATIONS WITH HIGH FLOW-RATES 12 Claims, 2 DrawingFigs.

[52] U.S. Cl 62/55.5 [5I] Int. Cl..... .t B01d S/00 [50] Field of Search62/55.5

[56] References Cited UNITED STATES PATENTS 2,703,673 3/1955 Winkler62/55.5

Primary ExamineF-William J. Wye Attorney- Young and Thompson ABSTRACT: Acryopump is constituted by a fluidtight casing inside which is arrangeda plurality of condensation plates carried by a cooling coil suppliedwith very cold fluid, the whole disposed externally of and around abaffle formed by a plurality of frustoconical rings arranged in theextension of a stop valve. The baffle is preferably cooled by amoderately cold fluid (80K) though conduits, while a coil embedded inthe wall of the casing and traversed by a moderately cold fluid cools aninternal wall of the casing. This cryopumping device is adapted toextract high flow rates at a relatively moderate pressure of theorder ofl0l2 torr.

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CRYOPUMHNG INSTALLA'HONS Wl'llll HlGlli FLOW- RATES The presentinvention relates to improvements in cryopumping installations with highflow rates, and in particular to such installations which can operatecontinuously up to moderately high vacua, of the order of lOz torr, forexample.

ln cryopumps, by means of which a vacuum can be obtained and thenmaintained in a chamber, the gas coming from the chamber to be exhaustedis deposited in the solid state on collecting means, constituted forexample by a condensation or sublimation surface cooled by the vapors ofa liquefied gas or by a refrigerator working in a closed circuitAPeriodically, after having stopped and isolated the pump from thechamber, it is necessary to regenerate the cryopump by heating thecondensation surface so as to liquefy or sublimate the solid deposit andto ensure the elimination of this latter by simple evacuation or drawingoff. lf the pumping of a chamber is to be effected continuously, twocryopumps are then arranged in parallel, one being in course ofregeneration while the other is in operation.

Up to the present time, cryopumps have been especially utilized forultravacua, that is to say for high vacua which may attain 1019 tori'Aln this case, the mass flow is very low and the thickness of thecondensate always remains small, even if the condensation surface isrelatively modest, and although this type of cryopump may be inoperation for long periods in order to maintain a very high vacuum, suchcontinuous working does not present any problems since it is notnecessary to carry out regeneration operations. The ultravacuumcryopumps constructed at the present time are thus characterized by thcexistence of a single pumping element or unit, and by condensation wallshaving a relatively modest surface area.

On the other hand, when the depression level is much less considerable,for example of the order of lO12 torr, the mass flow then becomes largeand the volume of condensate deposited in a given time is relativelyhigh. When the thickness of the condensate increases, the thermalexchanges between the gas to be solidified and the condensation surfacedeteriorate and this results in a reduction of the speed of pumpingtogether with a rise in the limiting pressure. In order to reduce theeffect of this additional thickness of condensate, it is then necessaryto increase the surface area of the heat-exchange walls and toregenerate the cryopump from time to time. It thus becomes necessary toarrangeA two cryopumps which operate cyclically.

The high value of the mass flow of gas to be cryopumped necessitates theproduction of a pumping unit which has at the same time a good inletconductance for the gases to be collected and a large condensationsurface area, and it is an object ofthe invention to provide a cryopumpin which these two characteristics are arranged so as to obtainsatisfactory operation of the pump with however a comparatively smalloverall size.

According to an essential characteristic feature of the invention, thecollecting means comprise main collecting means brought to a coldtemperature, arranged outside and around a baffle brought to amoderately cold temperature and constituted by an assembly of walls ofrevolution arranged at a distance from each other along a common axisforming an extension of the axis of the inlet valve, and having aninternal diameter substantially in the vicinity of that of the saidinlet valve. The baflle is a body composed of a plurality of deflectingwalls, for example of frustoconical shape, arranged at a distance fromeach other along a common axis and permitting a radial distribution insteps towards the exterior of the gas which passes into the interior ofthe baffle, while forming a screen against direct radiation coming fromthe zone at ambient temperature, that is to say in the present case,essentially from the inlet valve.

The advantages of this arrangement are as follows:

The cross section of passage of the baffle, that is to say the sum ofthe individual sections between two frustoconical walls, is independentof the diameter of the valve, and it can easily be increased byproviding a larger number of baffle walls, or in other words byextending the cryopump axially. lt is thus possible to obtain a veryhigh inlet conductance of the gases in the direction of the maincondensation surface.

The surface area of the condensation wall may be very large, since thelatter surrounds the baffle. Furthermore, a small increase in externaldiameter is sufficient to produce a very large increase in the exchangesurfaces.

ln the case of an installation which operates continuously with twopumping units, the regeneration of one cryopump unit is effected byintroducing into the chamber a certain flow of hot gas which, by coolingand becoming liquefied, causes the sublimation or the liquefaction ofthe deposit. This method of regeneration is very simple, very rapid andpermits good recovery of frigories.

The characteristic features and advantages of the invention will befurther brought out in the description which follows below, given by wayof example with reference to the accompanying drawings, in which:

FIG. l is a diagrammatic view of the whole of a cryopumpinginstallation;

FIG. 2 is a view in cross section of a pumping unit according to theinvention.

The following description gives an example of construction of a cryopumpwhich can operate without interruption for several months, and which iscapable of pumping a large mass flow at a pressure of l0l2 torr.

The installation according to the invention is composed of acryogenerator l, two pumping units 2 and 3 and accessories permittingcontinuous working to be effected.

The cryogenerator l produces a certain frigorific output at twotemperature levels, which are respectively in the vicinity of 80 K and25 K. The frigories produced by the cryogenerator are conveyed to thepumping units by means of a circulation of two fluxes of gaseous heliumunder pressure, respectively through the outward and return conduits 4and S with stop valves 6 and 7 for the very cold fluid (25 K) andoutward and return conduits 8 and 9 for the moderately cold fluid (80l() towards the two pumping units 2 and 3, which are connected by theisolating valves 13 and 14 respectively to a chamber l2 in which avacuum is to be maintained.

As shown in FIG. 2, each pumping unit 2 (3) is constituted by afluidtight casing delimited towards the exterior by a wall with highheat insulation 21 composed of two parts 21a, 2lb

fitted into each other. Inside the casing is arranged an assembly ofcondensation surfaces constituted by plates 22 carried by a cooling coil23 which is supplied with a very cold fluid by the circuit of theconduits 4 and S.

These plates 22, of which there is a very large number, are for examplesquare with a 5 mm. side, a thickness of.l mm. and spaced apart by 3 cm.On each side of the plates 22 arev arranged, on one side a wall 25 fixedagainst the internal face of the wall of the casing 21a; on the otherside a baffle 26, cornposed of a plurality of frustoconical rings 26a,26b, 26e, 26d, arranged coaxially with the vertical axis of the casingin the extension of the axis of the isolating valve (13 (14) and flaredupwards. These rings 26a, 26h, 26e, 26d, are blackened so as to preventreflection of the radiation produced by the surfaces at ambienttemperature (especially the valves ll3 (14). The lower ring 26d isfollowed by a conical reflector 27, the apex of which is directedupwards.

These rings forming the baffle 26, the reflector 27, and also the walls2S are supplied with fairly cold fluid by a cooling coil, constituted,level with the baffle 26, by a plurality of con duits in the form ofopen rings 30a, 30b, 30C, 30d, the downstream extremity of one beingconnected to the upstream extremity of` the next following ring byvapillar element 28a, 28h, 23e, 28d, this latter supplying a ring 31 levelwith the reflector 27, while the return is effected by the conduit 28eand by a coil 32 embedded in the wall 2S, both supplied by the conduits9 of fairly cold fluid.

lt will be noted that the wall 25 is extended downwards by a bottomcollecting wall 29 with a funnel member 35 and having a portion in theform of a dome 34 with one or a number of laterial perforations 33.

The installation (see FlG. 1) further comprises accessories whichenablethe saturated unit to be regenerated, and which ensure thecontinuous operation of the installation. These accessories mainlycomprise: A pumping group 40 for the noncondensable gases, connected toa conduit 4l, 42, terminating at the bottom of each pumping unit 2, 3,through the intermediary of a valve 43 and 44 respectively. This group40 is intended to eliminate the gases which are only condensable at atemperature colder than the temperature of the main condensation walls22 (that is to say colder than 25 K). These gases are mainly hydrogenand helium. lt is particularly advisable to utilize a diffusion pumpassociated with a primary pump, in consequence of the relatively lowflow rate of the pressure level (about lI3 torr) and the nature of thegases.

A prevacuum pump 45 connected by the conduits 46, 47 to valves 48, 49,in the interior of each unit 2, 3. After each regeneration, the pressurerises in the unit to a fairly high value. Before being able to put thisunit back into operation, it is necessary to reduce the pressure to afew torrs. A primary pump is particularly well suited to this use.

A receptacle 50 intended to collect the liquefied gases andcommunicating by a valve with atmospheric air, and into which dischargesa pipe 5l connected by the conduits 52, 53 to valves 54 (55), FIG. 2 onthe funnel 35 at the bottom of each pumping .unit 2, 3. This receptacle50 permits the collection of the liquefied deposit during regeneration.It is possible to recover the frigories stored in this tank by immersingin it a coil 56 through which passes the helium coming from the head offairly cold fluid 8, 9.

The regeneration of the pumping unit is effected in the followingmanner: A regenerated unit 2 (or 3) is put in parallel with the unit 3(or 2) in course of operation, after which this unit 3 (or 2)respectively, is isolated by the valve 14 (or I3) respectively. Thecirculation of helium at very low temperature (25 K) is then interruptedto the unit 3 in course of regeneration, by closing the valve 7.

The valve 55 which puts the unit 3 into communication with the tank 50,is then opened. An inlet of dry atmosphere takes place which causes theliquefaction of the deposit. The liquid obtained is then collected bygravity in this same tank 50.

The unit 3 is then isolated from the tank 50 (closure of the valve 55)and is then put into communication with the prevacuum pump 45 by openingthe valve 48. The pressure is then brought to a value of a few torrs.During the same time, the unit is cooled by opening the valve 7, by asmall flow of helium at 25 K so as to prepare it for being put intooperation,

When the temperature of the cryosurface is lower than 30 K, the pumpingunit is regenerated and is immediately ready to work.

The installation described above, or any other installation derivedtherefrom, permits the production of a cryopump working continuously andcapable of pumping a large mass flow at pressures of the order of l0lztorr. It is possible to contemplate the use of this installation inreplacing pumping groups comprising Roots" or steam ejectors. Thereplacement of the Roots is particularly recommended when the gas to bepumped contains dust.

I claim:

1. A cryopump with a high flow rate, comprising a fluidtight casingthermally insulated from the exterior and having a wide inlet passage,an inlet valve associated with said passage, gas collectionmeanscomprising baffle means formed by an assembly of walls of annularform mounted at a distance from each other along a common axis in theextension of the axis of said inlet valve, said baffle means having aninternal diameter substantially close to that of said inlet passage,main collecting means disposed externally around said baffle, means andmeans for circulating a moderately cold fluid for said baffle means anda very cold fluid for said main collecting means.

2. A cryopump with a high flow rate as claimed in claim l, in which saidbaffle means comprises a plurality of frustoconical stepped walls,spaced apart from each other.

3. A cryopump as claimed in claim 2, in which said frustoconical wallsare mounted inside said casing so as to flare outwards towards theexterior in the direction of said inlet valve.

4. A cryopump with a high flow rate as claimed in claim l, in which saidmeans for circulating a very cold fluid comprise a tubular coil mountedround and externally to said baffle, means said main collecting meanscomprising an assembly of metal plates carried by said coil.

5. A cryopump with a high flow rate as claimed in claim l, and furthercomprising a reflector located at the extremity of said baffle meansopposite to said inlet valve, said means for circulating a moderatelycold fluid incorporating a tube for cooling said reflector.

6. A cryopump with a high flow rate as claimed in claim 1, in which saidmeans for circulating a very cold fluid comprise a fluid at atemperature substantially of the order of 25 K, while said means forcirculating a moderately cold fluid comprise a fluid at a temperaturesubstantially of the order of K.

7. A cryopump with a high flow rate as claimed in claim l, in which aninternal wall of said casing is cooled by said means for circulating amoderately cold fluid.

8. A cryopump with a high flow rate as claimed in claim 7, in which saidcasing is provided with a lower passage for the evacuation of liquid tothe exterior, and in which said intemal wall of the casing has a portionof funnel shape engaged in said liquid-evacuation passage.

9. A cryopump with a high flow rate as claimed in claim 7, in which saidcasing is provided with a lower passage for the evacuation of gasestowards the exterior, and in which said internal wall of the casing isadapted to form a dome perforated laterally above said gas-evacuationpassage.

l0. A cryopumping installation with a high flow rate, cornprising atleast two cryopumps each including a fluidtight casing thermallyinsulated from the exterior and having a wide inlet passage, an inletvalve associated with said passage, gas collection means comprisingbaffle means formed by an assembly of walls of annular form arranged ata distance from each other along a common axis in the extension of theaxis of said inlet valve, said baffle means having an internal diametersubstantially close to that of said inlet passage and main collectingmeans disposed externally of and around said baffle means, means forcirculating a moderately cold fluid for said baffle means and a verycold fluid for said main collecting means, a single chamber to beexhausted coupled to each said pump by means of each of said inletvalves, a double flux cryogenerator supplying said means for circulatingmoderately cold and very cold fluids, stop valves on said circulatingmeans, a pumping group, coupling means incorporating stop valves betweensaid pumping group and each said cryopump, a prevacuum pump, couplingmeans including stop valves between said prevacuum group and each saidcryopump, and means for recovery of liquids adapted to cooperate withsaid means for circulating the moderately cold fluid.

ll. A cryopump with a high flow rate as claimed in claim l, said annularbaffle means being so shaped and disposed as to direct gas from withinsaid annular baffle means radially outwardly toward said main collectingmeans.

12. A cryopump with a high flow rate as claimed in claim 1l, in whichsaid main collecting means comprises a large number of metal plates.

2. A cryopump with a high flow rate as claimed in claim 1, in which saidbaffle means comprises a plurality of frustoconical stepped walls,spaced apart from each other.
 3. A cryopump as claimed in claim 2, inwhich said frustoconical walls are mounted inside said casing so as toflare outwards towards the exterior in the direction of said inletvalve.
 4. A cryopump with a high flow rate as claimed in claim 1, inwhich said means for circulating a very cold fluid comprise a tubularcoil mounted round and externally to said baffle, means said maincollecting means comprising an assembly of metal plates carried by saidcoil.
 5. A cryopump with a high flow rate as claimed in claim 1, andfurther comprising a reflector located at the extremity of said bafflemeans opposite to said inlet valve, said means for circulating amoderately cold fluid incorporating a tube for cooling said reflector.6. A cryopump with a high flow rate as claimed in claim 1, in which saidmeans for circulating a very cold fluid comprise a fluid at atemperature substantially of the order of 25* K, while said means forcirculating a moderately cold fluid comprise a fluid at a temperaturesubstantially of the order of 80* K.
 7. A cryopump with a high flow rateas claimed in claim 1, in which an internal wall of said casing iscooled by said means for circulating a moderately cold fluid.
 8. Acryopump with a high flow rate as claimed in claim 7, in which saidcasing is provided with a lower passage for the evacuation of liquid tothe exterior, and in which said internal wall of the casing has aportion of funnel shape engaged in said liquid-evacuation passage.
 9. Acryopump with a high flow rate as claimed in claim 7, in which saidcasing is provided with a lower passage for the evacuation of gasestowards the exterior, and in which said internal wall of the cAsing isadapted to form a dome perforated laterally above said gas-evacuationpassage.
 10. A cryopumping installation with a high flow rate,comprising at least two cryopumps each including a fluidtight casingthermally insulated from the exterior and having a wide inlet passage,an inlet valve associated with said passage, gas collection meanscomprising baffle means formed by an assembly of walls of annular formarranged at a distance from each other along a common axis in theextension of the axis of said inlet valve, said baffle means having aninternal diameter substantially close to that of said inlet passage andmain collecting means disposed externally of and around said bafflemeans, means for circulating a moderately cold fluid for said bafflemeans and a very cold fluid for said main collecting means, a singlechamber to be exhausted coupled to each said pump by means of each ofsaid inlet valves, a double flux cryogenerator supplying said means forcirculating moderately cold and very cold fluids, stop valves on saidcirculating means, a pumping group, coupling means incorporating stopvalves between said pumping group and each said cryopump, a prevacuumpump, coupling means including stop valves between said prevacuum groupand each said cryopump, and means for recovery of liquids adapted tocooperate with said means for circulating the moderately cold fluid. 11.A cryopump with a high flow rate as claimed in claim 1, said annularbaffle means being so shaped and disposed as to direct gas from withinsaid annular baffle means radially outwardly toward said main collectingmeans.
 12. A cryopump with a high flow rate as claimed in claim 11, inwhich said main collecting means comprises a large number of metalplates.